Calcium hypochlorite composition

ABSTRACT

A granular, heterogeneous calcium hypochlorite composition comprising a mixture of a substantially anhydrated granular component and a hydrated granular component keeping the crystallization water of from 2 to 3 moles water per mole of Ca(OCl) 2  in the form of Ca(OCl) 2 .3H 2  O has an improved stability and safety, and said composition is suitable for preparing break-resistant, good-dissoluble calcium hypochlorite tablets.

BACKGROUND OF THE INVENTION

This invention relates to an improved calcium hypochlorite compositionand, more particularly, this invention concerns a calcium hypochloritecomposition having an improved storage stability and the safety, i.e.,which resists to spontaneous decomposition and self-propagatingdecomposition.

BRIEF DESCRIPTION OF THE PRIOR ART

It is said that calcium hypochlorite compositions which are commerciallyhandled as the high-grade calcium hypochlorite composition generallycontain about 65 to 75% of calcium hypochlorite Ca(OCl)₂ !, about 15 to20% of chlorides and about 5 to 7% of alkalis, and the water content isgenerally less than 2%. The composition decomposes when it is subjectedto heating or contacted with organic materials of easily oxidizednature, and the decomposition is exothermic and proceeds rapidly. Evenunder normal storage conditions of ambient temperatures, calciumhypochlorite in the composition decomposes gradually and will lose 3 to5% of the available chlorine content in a year.

Several processes have been proposed for making the calcium hypochloritecomposition safe, and one of the most promising means is said to makehold a proper amount of water in the composition.

One process (U.S. Pat. No. 3,645,005) teaches a composition containing 6to 15% of water for a calcium hypochlorite composition that is resistantto self-propagating decomposition with the storage stability comparablewith that of substantially dry compositions.

Another process (Japanese Kokai 75-70297) teaches the water content of16 to 22% for a composition having an excellent safety.

In so far as safety of the composition is concerned, these teachings canfacilitate the object of making it safer, however, the storage stabilityof the former is not entirely satisfactory as shown in Test 1, and thelatter composition has a difficulty in obtaining a composition of highavailable chlorine content.

OBJECT OF THE INVENTION

It is the object of this invention to provide a calcium hypochloritecomposition resisting to the self-propagating decomposition and havingan improved storage stability of as stable as a substantially anhydratedcalcium hypochlorite composition.

Another object of this invention is to provide a calcium hypochloritecomposition containing a high available chlorine.

Other objects and advantages of this invention will further becomeapparent hereinafter.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a relationship between the water content of calciumhypochlorite compositions and the corresponding rate of loss ofavailable chlorine contents when the compositions were storaged underdifferent conditions.

FIG. 2, FIG. 3 and FIG. 4 show X-ray diffraction diagrams of calciumhypochlorite compositions.

DETAILED DESCRIPTION

The present invention is a calcium hypochlorite composition composed ofa heterogeneous mixture of a hydrated granular calcium hypochloritecomposition and an anhydrated granular calcium hypochlorite composition,which has an excellent storage stability and safety.

The configurations of the hydrated component and the anhydratedcomponent are preferably granular composed of particles ranging from 8to 100 mesh.

Said hydrated component is a calcium hypochlorite composition having theavailable chlorine of at least 50%, and the water kept in thecomposition is all crystallization water to form Ca(OCl)₂.3H₂ O. Theamount of said crystallization water is calculated to be from 2 to 3moles per mole of Ca(OCl)₂, and the active ingredient is completelycrystallines of Ca(OCl)₂.3H₂ O or crystallines of Ca(OCl)₂.3H₂ Opartially accompanied with crystallines of Ca(OCl)₂.

Said hydrated component is characterized structurally by comparing theX-ray diffraction diagrams as follows:

FIG. 2 (diagram of a hydrated calcium hypochlorite composition of thepresent invention) indicates the existence of Ca(OCl)₂.3H₂ O mainly.

FIG. 3 (diagram of an anhydrated calcium hypochlorite composition)indicates existence of Ca(OCl)₂ mainly.

FIG. 4 (diagram of a hydrated calcium hypochlorite composition preparedby the prior art and containing 6% of water) indicates the coexistenceof Ca(OCl)₂.3H₂ O and Ca(OCl)₂ intermediately.

The hydrated component is preferably obtained at an early step of thedrying process of wet neutral calcium hypochlorite crystals which areseparated from a slurry of chlorinated mixture in commercial productionof the high-grade calcium hypochlorite.

Said anhydrated component is a calcium hypochlorite composition which isavailable as commercial high-grade calcium hypochlorite compositionscontaining about 65-75% of available chlorine and less than 2% ofcrystalization water.

The objective of the invention can be achieved based on a discovery thatsaid anhydrated component which is satisfactorily stable but regretfullyunsafe can be improved in its defect of the safety when it is combinedproperly with said hydrated component which is not only surprisinglyresistant to the self-propagrating decomposition but also fairly stableat ordinary temperatures.

The proportion of the hydrated component to the anhydrated componentvaries in accordance with properties of the hydrated component, and issettled in consideration of the safety of the blended composition.Blending of 0.3 parts by weight or more of the hydrated component with 1part of the anhydrated component provides a safe composition preventedfrom the self-propagating decomposition, as exhibited in Test 2. Ahydrated component keeping an amount of said crystallization watercorresponding to nearly 3 moles per mole of Ca(OCl)₂ is preferablyemployed for providing most efficiently the component with the safetyproperty, however, such easily obtainable hydrated components as keepingan amount of said crystallization water corresponding to 3.0 - 2.5 molesper mole of Ca(OCl)₂ are also employed.

The blending of the components is conducted by means of suchconventional mixing apparatus as ribbon blenders and flash mixers.

The fact that the water kept in the hydrated component of a compositionof the present invention does not transfer to the anhydrated component,as shown in Test 3, makes the composition to be a heterogeneous mixtureof two different granular components.

The composition of the invention is fortified in its available chlorinecontent to more than about 55% and has the safety property of resistantto self-propagating decomposition, and is superior to compositionsprepared by the prior art in respect to its storage stability.

The present composition is composed of the specific hydrated calciumhypochlorite composition and the anhydrated calcium hypochloritecomposition both of which generate during their spontaneousdecomposition smaller amount of chlorine gas than usual hydrated calciumhypochlorite composotions, and the amount of chlorine gas generated fromthe present composition is also smaller than that from compositionsprepared by the prior art. The fact shows merits in corrosion ofmetallic containers for the calcium hypochlorite composition.

A further independent advantage of the invention concerns calciumhypochlorite composition tablets of improved properties. Since thecomposition is composed of an anhydrated component which dissolvesslowly in water and a hydrated component which dissolves easily, thecombined dissolution characteristics of the composition provide a wellbalanced prolonged sterilizing effect in its application for watertreatment. Calcium hypochlorite compositions are formed in the tabletconfiguration by molding granular compositions with a molding press. Thetablet is usually molded with higher pressures to make it resistant tobreakage during shipment and dissolution, therefore, such tablet tendsto become more slowly in its dissolution in water. Accordingly, thetablet having a good dissolution property and being strong enough towithstand breakage during the shipment is desired.

Since the calcium hypochlorite composition of the invention contains ahydrated composition which can be molded firmly with a high pressuremolding into tablets without reducing the dissolution property, thecalcium hypochlorite composition of the present invention provides atablet which is not only safe in manufacturing and in handling andstable but also resistant to breakage with controlled dissolutioncharacteristics.

The following examples may serve further to explain the invention, butare not to be construed as imposing any limitations thereon.

EXAMPLE 1

30 kg of a hydrated granular calcium hypochlorite composition having64.7% of available chlorine content and crystallization watercorresponding to 2 moles per mole of Ca(OCl)₂, and 18 kg of ananhydrated granular calcium hypochlorite composition having 71.3% ofavailable chlorine content and 0.9% of crystallization water contentwere mixed intimately with a ribbon blender to obtain 48 kg of agranular heterogeneous calcium hypochlorite composition having 67.1% ofavailable chlorine content. The composition did not decompose by a litmatch. The obtained composition was storaged under the conditions of 1year at ambient temperatures, 200 days at 30° C. and 50 days at 40° C.,and rates of loss of the available chlorine content during the storagewere measured to result 4.4, 10.8 and 7.2% respectively.

EXAMPLE 2

20 kg of a hydrated granular calcium hypochlorite composition having58.1% of available chlorine content and crystallization watercorresponding to 3 moles per mole of Ca(OCl)₂, and 30 kg of ananhydrated granular calcium hypochlorite composition having 71.7% ofavailable chlorine content and 1.2% of crystallization water contentwere mixed to obtain 50 kg of a granular heterogeneous calciumhypochlorite composition having 66.3% of available chlorine content. Thecomposition did not decompose by a lit match. The rates of loss of theavailable chlorine content of the obtained composition measured afterstorage conditions of 1 year at ambient temperatures, 200 days at 30° C.and 50 days at 40° C. were 4.5, 10.5 and 7.0% respectively.

EXAMPLE 3

A hydrated granular calcium hypochlorite composition having 55.3% ofavailable chlorine content and crystallization water corresponding to2.9 moles per mole of Ca(OCl)₂ were mixed with 1 part by weight of ananhydrated granular calcium hypochlorite composition having 73.5% ofavailable chlorine content and 0.4% of crystallization water content toobtain the following granular heterogeneous calcium hypochloritecompositions.

Composition

(A): 0.3 parts of the hydrated component was mixed. Available chlorinecontent was 69.3%.

(B): 0.5 parts of the hydrated component was mixed. Available chlorinecontent was 67.4%.

(C): 0 (The anhydrated component itself)

The compositions were compression molded with a molding press to obtaintablets of about 30 mm in diameter, 15 mm in high and 20 g in weight.The compression hardness of the tablets measured with a uniaxialcompression tester were 120 kg on the avarage for tablets.

Each of the tablet was dissolved in 3l of water maintained at 30° C.under agitation of 60 RPM to measure the time necessary for completedissolution of the tablet. The result is as follows:

Tablet from Composition

(A): 140 min.

(B): 120

(c): 190

the tablets were subjected to a safety test of an ignition with 2 dropsof glycerine dropped on the tablets at 50° C. Result of the safety testis as follows:

Tablet from Composition

(A): Decomposed after 20 seconds and propagated slowly, but stoppedshortly. (No decomposition when tested at ambient temperatures)

(B): No decomposition

(C): Decomposed after 15 seconds with flash, and the decompositionspread wholly.

Test 1

A hydrated calcium hypochlorite composition having 75% of availablechlorine on a basis of the anhydrated state was anhydrated by contactingit with hot dry air to prepare specimens of granular calciumhypochlorite compositions which differed in their crystallization watercontents in the range of from about 22 to about 1%. These specimens werestoraged under different conditions, and the relationship between therate of loss of available chlorine content and the water content of thecomposition was checked.

The result indicating a striking effect of crystallization water contenton stability of calcium hypochlorite composition is as shown in FIG. 1,where the storage conditions were as follows;

I. Ambient temperatures for 1 year,

II. 40° C. for 50 days, and

III. 30° C. for 200 days

Test 2

A hydrated granular calcium hypochlorite composition having 60.4% ofavailable chlorine content and crystallization water corresponding to 3moles per mole of Ca(OCl)₂ was employed as an example of the hydratedcomponent.

Various parts by weight of the hydrated component was mixed with 1 partof an anhydrated granular calcium hypochlorite composition having 76.5%of available chlorine and 0.4% of crystallization water content.Specimens of the mixture were subjected to safety tests of calciumhypochlorite compositions, and the result is as mentioned below:

    ______________________________________                                        Parts of the                                                                  hydrated  Ignition test Ignition test with                                    component with match*   glycerine**                                           ______________________________________                                        0         Self-propagating                                                                            Decomposed after 3                                              decomposition of                                                                            seconds and propagated                                          24 cm/min speed.                                                                            at 21 cm/min speed.                                   0.1       Self-propagating                                                                            Decomposed after 7                                              decomposition of                                                                            seconds and propagated                                          10 cm/min speed.                                                                            at 9 cm/min speed.                                    0.2       Self-propagating                                                                            At the drop point,                                              decomposition of                                                                            decomposition continued                                         6 cm/min speed.                                                                             for 5 seconds.                                        0.3       No decomposition                                                                            No decomposition                                      ______________________________________                                         *about 100 g of a specimen was placed on a U-type iron trough of 50 cm        length and 10 cm width. The specimen was lit with a match at the end.         **Two drops of glycerine were dropped at end of the specimen placed in th     same way as the above test.                                              

Further, a hydrated granular calcium hypochlorite composition having57.5% of available chlorine content and crystallization watercorresponding to 2.2 moles per mole of Ca(OCl)₂ was employed as anexample of the hydrated component. The hydrated component was mixed withan anhydrated granular calcium hypochlorite composition having 73.4% ofavailable chlorine and 0.6% of crystallization water content in variedproportions per 1 part of the anhydrated component. Specimens of themixture were subjected to the same safety test as the above.

The test resulted in a mixture composed of 0.7 parts or more of thehydrated component and 1 part of the anhydrated component showed nodecomposition.

Test 3

Following 4 specimens of calcium hypochlorite composition were employedto check a transfer of water between the hydrated component and theanhydrated component.

    ______________________________________                                                     Available Crystalliza-                                           Calcium hypochlorite                                                                       chlorine  tion water Range of                                    composition  content   condition  particle size                               ______________________________________                                        (A)          60.1%     2.9 moles* 14 -  20 mesh                               (B)          "         "          20 - 42                                     (C)          73.5      1.0%**     14-  20                                     (D)          "         "          20-  42                                     ______________________________________                                         *Corresponding crystallization water, moles per mole of Ca(OCl).sub.2         **Crystallization water content                                          

Equal amount of (A) and (D) or (B) and (C) were mixed, and the mixturewas storaged at 30° C. for a length of time. After the storage, themixtures were sieved with a 20 mesh sieve to obtain the components asthe retained and the passed, which corresponded to (A) or (C) and (B) or(D) respectively. Crystallization water condition of each component wasas mentioned below:

    ______________________________________                                                    Water condition                                                                          Water condition                                                    of mesh passed                                                                           of 20 mesh retained                                                particles  particles                                              ______________________________________                                        Mixture of (A) and (D):                                                       After 30 days   0.8%         2.87 moles                                       After 60 days   1.0          2.88                                             After 90 days   1.0          2.87                                             Mixture of (B) and (C):                                                       After 30 days   2.88 moles   1.0%                                             After 60 days   2.9          1.0                                              After 90 days   2.88         0.9                                              ______________________________________                                    

We claim:
 1. A heterogenous mixture of at least 0.3 parts by weight of(A) and 1 part by weight of (B), which comprises a stable, safe,granular calcium hypochlorite composition containing at least about 55%of available chlorine; where(A) is a hydrated calcium hypochloritecomposition containing more than about 50% of available chlorine andkeeping an amount of crystallization water corresponding to from 2 to 3moles per mole of Ca(OCl)₂ in the form of Ca(OCl)₂.3H₂ O, and (B) is ananhydrated calcium hypochlorite composition containing about 65% or moreof available chlorine and less than 2% of crystallization water.
 2. Thecomposition according to claim 1 wherein the amount of crystallizationwater kept in a hydrated calcium hypochlorite composition corresponds tofrom 2.5 to 3.0 moles per mole of Ca(OCl)₂.
 3. The composition accordingto claim 1 wherein the amount of crystallization water kept in ahydrated calcium hypochlorite composition corresponds to from 2.8 to 3.0moles per mole of Ca(OCl)₂.
 4. The composition according to claim 1, theactive ingredient of a hydrated calcium hypochlorite composition issubstantially Ca(OCl)₂.3H₂ O.
 5. A stable, safe, break-resistant,good-dissolubable calcium hypochlorite composition tablet containing atleast about 55% of available chlorine which is prepared by compressionmolding of a heterogeneous mixture of at least 0.3 parts by weight of(A) and 1 part by weight of (B), where(A): a hydrated calciumhypochlorite composition containing more than about 50% of availablechlorine and keeping an amount of crystallization water corresponding tofrom 2 to 3 moles per mole of Ca(OCl)₂ in the form of Ca(OCl)₂.3H₂ O,and (B): an anhydrated calcium hypochlorite composition containing about65% or more of available chlorine and less than 2% of crystallizationwater.
 6. The composition according to claim 5 wherein the amount ofcrystallization water kept in a hydrated calcium hypochloritecomposition corresponds to from 2.5 to 3.0 moles per mole of Ca(OCl)₂.7. The composition according to claim 5 wherein the amount ofcrystallization water kept in a hydrated calcium hypochloritecomposition corresponds to from 2.8 to 3.0 moles per mole of Ca(OCl)₂.8. The composition according to claim 5, the active ingredient of ahydrated calcium hypochlorite composition is substantially Ca(OCl)₂.3H₂O.